.\" Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
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.\" Portions of this text are reprinted and reproduced in electronic form
.\" from IEEE Std 1003.1, 2004 Edition, Standard for Information Technology --
.\" Portable Operating System Interface (POSIX), The Open Group Base
.\" Specifications Issue 6, Copyright (C) 2001-2004 by the Institute of
.\" Electrical and Electronics Engineers, Inc and The Open Group.  In the
.\" event of any discrepancy between this version and the original IEEE and
.\" The Open Group Standard, the original IEEE and The Open Group Standard is
.\" the referee document.  The original Standard can be obtained online at
.\"	http://www.opengroup.org/unix/online.html.
.\"
.Dd September 21, 2016
.Dt POSIX_OPENPT 2
.Os
.Sh NAME
.Nm posix_openpt
.Nd "open a pseudo-terminal device"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In fcntl.h
.In stdlib.h
.Ft int
.Fn posix_openpt "int oflag"
.Sh DESCRIPTION
The
.Fn posix_openpt
function allocates a new pseudo-terminal and establishes a connection
with its master device.
A slave device shall be created in
.Pa /dev/pts .
After the pseudo-terminal has been allocated, the slave device should
have the proper permissions before it can be used (see
.Xr grantpt 3 ) .
The name of the slave device can be determined by calling
.Xr ptsname 3 .
.Pp
The file status flags and file access modes of the open file description
shall be set according to the value of
.Fa oflag .
Values for
.Fa oflag
are constructed by a bitwise-inclusive OR of flags from the following
list, defined in
.In fcntl.h :
.Bl -tag -width ".Dv O_CLOEXEC"
.It Dv O_RDWR
Open for reading and writing.
.It Dv O_NOCTTY
If set
.Fn posix_openpt
shall not cause the terminal device to become the controlling terminal
for the process.
.It Dv O_CLOEXEC
Set the close-on-exec flag for the new file descriptor.
.El
.Pp
The
.Fn posix_openpt
function shall fail when
.Fa oflag
contains other values.
.Sh RETURN VALUES
Upon successful completion, the
.Fn posix_openpt
function shall allocate a new pseudo-terminal device and return a
non-negative integer representing a file descriptor, which is connected
to its master device.
Otherwise, -1 shall be returned and errno set to indicate the error.
.Sh ERRORS
The
.Fn posix_openpt
function shall fail if:
.Bl -tag -width Er
.It Bq Er ENFILE
The system file table is full.
.It Bq Er EINVAL
The value of
.Fa oflag
is not valid.
.It Bq Er EAGAIN
Out of pseudo-terminal resources.
.El
.Sh SEE ALSO
.Xr ptsname 3 ,
.Xr pts 4 ,
.Xr tty 4
.Sh STANDARDS
The
.Fn posix_openpt
function conforms to
.St -p1003.1-2001 .
The ability to use
.Dv O_CLOEXEC
is an extension to the standard.
.Sh HISTORY
The
.Fn posix_openpt
function appeared in
.Fx 5.0 .
In
.Fx 8.0 ,
this function was changed to a system call.
.Sh NOTES
The flag
.Dv O_NOCTTY
is included for compatibility; in
.Fx ,
opening a terminal does not cause it to become a process's controlling
terminal.
.Sh AUTHORS
.An \&Ed Schouten Aq Mt ed@FreeBSD.org
